With ever increasing demand for communication services, and the crowding of conventionally assigned spectrum, governments are allowing unlicensed communication operation in licensed, but under-utilized spectrum bands. One example of this is the recent Federal Communications Commission's decision to allow radio communication systems to use channels in the spectrum region designated for licensed television broadcast. In a given geographic region, there will typically be a number of television channels which are not presently being utilized for television or wireless microphone transmission. These unused wideband 6 MHz channels may be made available for broadband, wideband or narrowband radio communication which may be 12.5 KHz to 150 KHz wide. Accordingly, there is a need to identify spectrum segments or channels conventionally licensed or utilized for one form of communication that may be used for other, secondary communication activity.
To determine the availability of a given channel or channels, a secondary communication system will task a number of nodes associated with the system to sense the channels, and report the results. The sensing results allow the communication system to determine whether the sensed channel(s) are available for secondary communication, or if the communication should search elsewhere for available channels. To assure the secondary communication activity will not interfere with primary communication operators, the set of nodes tasked with sensing the channel(s) should be geographically or spatially diverse within the coverage area of the secondary communication system. Many modern communication devices are equipped with satellite positioning receivers and are able to determine and report their own location. Knowing the locations of nodes in the system makes selecting nodes to provide adequate geographic diversity relatively easy, but in systems where there is no node location information available, such as when the nodes do not have a self location determination means, selecting nodes that have adequate geographic diversity becomes challenging. Therefore, there is a need to select a set of nodes having a desired level of geographic diversity to assure adequate sensing results when searching for an available channel in a secondary communication system.